"""Alembic environment configuration for database migrations.

Configures offline and online migration contexts using SQLAlchemy
and the target metadata defined in db_async.metadata.
"""
import os
from logging.config import fileConfig

from sqlalchemy import engine_from_config, pool
from alembic import context

    # Alembic Config object provides access to values in the .ini file
config = context.config

  # Override sqlalchemy.url with DATABASE_URL environment variable if provided
database_url = os.getenv('DATABASE_URL', config.get_main_option('sqlalchemy.url'))
config.set_main_option('sqlalchemy.url', database_url)

# Set up Python logging according to config file
if config.config_file_name is not None:
    fileConfig(config.config_file_name)

# add your model's MetaData object here
# for 'autogenerate' support
from db_async import metadata  # noqa
target_metadata = metadata


def run_migrations_offline():
    """Run migrations in 'offline' mode using literal SQL script generation."""
    url = config.get_main_option('sqlalchemy.url')
    context.configure(
        url=url,
        target_metadata=target_metadata,
        literal_binds=True,
        dialect_opts={"paramstyle": "named"},
    )

    with context.begin_transaction():
        context.run_migrations()


def run_migrations_online():
    """Run migrations in 'online' mode against a live database connection."""
    connectable = engine_from_config(
        config.get_section(config.config_ini_section),
        prefix='sqlalchemy.',
        poolclass=pool.NullPool,
    )

    with connectable.connect() as connection:
        context.configure(
            connection=connection,
            target_metadata=target_metadata,
        )

        with context.begin_transaction():
            context.run_migrations()


if context.is_offline_mode():
    run_migrations_offline()
else:
    run_migrations_online()